Hollow-base blackpowder bullets

[bladeracer]

How do you ensure the hollow-based bullets don't leave a cavity over the powder charge?
We're constantly warned that you must not leave any air gap in a blackpowder firearm, so I've often wondered how hollow-based bullets work. Does seating the bullet the same as with a ball force it down into the charge such that it doesn't need to be worried about, or do these bullets require some deftness?

[perentie]

I would not worry too much. I dont use hollow base when paper patching but when breech seating I leave a 1/8 th inch air gap between the bullet and the mouth of the case. Your air space would be less than that. bigger gaps yes, may run the risk of ringing.

[Noisydad]

That tiny amount of air wouldn’t have any effect. I’m currently shooting my .58 Muzzle loader with 580 gn Minnie’s that have quite a deep cavity which I’m not filling with lube as some do. Haven’t blown it up yet after hundreds and hundreds of shots.

[No1_49er]

The hollow base was generally there to ensure a good "upset" of the skirt into the rifling. If you go back to the time of the 577-450, a plug formed of wax and clay was used to partially fill that cavity and so promote obturation.
With muzzle loading, the "cartridge" was wrapped in paper: The end was torn off, powder dumped down the bore, paper stuffed in the bore, then the bullet (minnie) pressed down on the load. The paper filled that cavity and probably helped with the obturation.
Check out the Martini forums etc.

[No1Mk3]

G'day bladeracer,
Don't be too concerned about air gaps, whilst it is not a good idea to have a large air gap that will compress prior to moving the projectile and potentially add a pressure spike, it does (and in the old days did often) happen. One problem with gaps, as pertains to black, is room for the powder to uncover the primer/flash source and suffer secondary ignition but this needs a quite large space. (The same principle applies to fast powders in large capacity cartridge cases) What you will get from a Minie isn't a concern at all, but I do use that space for a grease cookie, Cheers.

[bladeracer]

That tiny amount of air wouldn’t have any effect. I’m currently shooting my .58 Muzzle loader with 580 gn Minnie’s that have quite a deep cavity which I’m not filling with lube as some do. Haven’t blown it up yet after hundreds and hundreds of shots.

Yes, I guess it's really little different to seating a ball as well, now that I think about it